Embodiments of the present invention make use of Raman spectral data obtained from a sample in response to illuminating the sample with light. Raman spectroscopy is an effective tool for identifying and characterizing a vast array of molecules. In Raman spectroscopy, a sample is illuminated with light typically from a laser and of a known wavelength (typically visible, or near infrared, but also ultraviolet). The laser light (also sometimes referred to as the Raman pump) interacts with the electron clouds in the molecules of the specimen and, as a result of this interaction, experiences selected wavelength shifting representing differences between the vibrational and/or rotational energy levels of the molecule. The precise nature of this wavelength shifting depends upon the molecules present in the specimen and can include both a Stokes shift (where the emitted photon is of longer wavelength than the incident or illuminating photon) and an anti-Stokes shift (where the emitted photon is of shorter wavelength than the incident photon). However, because they arise from molecules in excited vibration states, anti-Stokes spectra are lower in intensity than Stokes spectra, and also diminish in intensity with greater anti-Stokes shifts. A unique wavelength signature (typically called the Raman signature, or Raman spectrum) is produced by each molecule. This unique Raman signature permits the molecule to be identified and characterized. More specifically, the spectrum of light returning from the specimen is analyzed with an optical spectrometer so as to identify the Raman-induced wavelength shifting of the Raman pump light, and then this resulting Raman spectrum is compared (for example, by a processor) with a library of known Raman signatures so as to identify a molecule in the sample. Raman theory, including the Stokes/anti-Stokes ratio is described, for example, in D. A. Long, “Raman Spectroscopy”, McGraw-Hill, 1977, particularly at pages 82-84.
Raman spectroscopy may include Surface Enhanced Raman Spectroscopy (“SERS”) where the reflective surface is reflective, and enhances the Raman signal in a manner known for SERS surfaces. Principles and different techniques of SERS spectroscopy are described, for example, in US20120287427, U.S. Pat. No. 8,241,922, U.S. Pat. No. 7,450,227, WO/2006/137885, and elsewhere. In any embodiment the sample of interest may be a solid, or a fluid, such as a gas or liquid
Raman spectroscopy is widely used in scientific, commercial and public safety areas. Recent technological advances have made it possible to significantly reduce the size and cost of Raman spectroscopy systems. This has in turn increased the range of practical applications for Raman spectroscopy. For example, portable units have recently become available for various field uses, such as the on-site identification of potentially hazardous substances. Details of analyzers using Raman spectroscopy and spectra interpretation can be found, for example, in U.S. Pat. No. 8,107,069, U.S. Pat. No. 8,081,305, U.S. Pat. No. 7,928,391, U.S. Pat. No. 7,701,571, U.S. Pat. No. 7,636,157, U.S. Pat. No. 8,107,069, and U.S. patent publications US2009/0213361, US2010/0191493, US2010/0315629 (all of which references are incorporated herein by reference), and elsewhere. The design of Raman spectrometers, including discussions of lasers and detectors, is also described in Richard L. McCreery, “Raman Spectroscopy for Chemical Analysis”, Wiley-Interscience, 2000.